diff --git a/amaranth/hdl/_ir.py b/amaranth/hdl/_ir.py
index 075991a..f9bec3d 100644
--- a/amaranth/hdl/_ir.py
+++ b/amaranth/hdl/_ir.py
@@ -71,6 +71,7 @@ class Fragment:
         self.src_loc = src_loc
         self.origins = None
         self.domains_propagated_up = {}
+        self.domain_renames = {}
 
     def add_domains(self, *domains):
         for domain in flatten(domains):
@@ -655,6 +656,19 @@ class Design:
             subfragment_name = _add_name(frag_info.assigned_names, subfragment_name)
             self._assign_names(subfragment, hierarchy=(*hierarchy, subfragment_name))
 
+    def lookup_domain(self, domain, context):
+        if domain == "comb":
+            raise KeyError("comb")
+        if context is not None:
+            try:
+                fragment = self.elaboratables[context]
+            except KeyError:
+                raise ValueError(f"Elaboratable {context!r} is not a part of the design")
+        else:
+            fragment = self.fragment
+        domain = fragment.domain_renames.get(domain, domain)
+        return fragment.domains[domain]
+
 
 ############################################################################################### >:3
 
diff --git a/amaranth/hdl/_xfrm.py b/amaranth/hdl/_xfrm.py
index c1d12a1..062cddc 100644
--- a/amaranth/hdl/_xfrm.py
+++ b/amaranth/hdl/_xfrm.py
@@ -252,6 +252,9 @@ class FragmentTransformer:
             for domain, statements in fragment.statements.items():
                 new_fragment.add_statements(domain, statements)
 
+    def map_domain_renames(self, fragment, new_fragment):
+        new_fragment.domain_renames = dict(fragment.domain_renames)
+
     def map_memory_ports(self, fragment, new_fragment):
         if hasattr(self, "on_value"):
             for port in new_fragment._read_ports:
@@ -318,6 +321,7 @@ class FragmentTransformer:
         self.map_subfragments(fragment, new_fragment)
         self.map_domains(fragment, new_fragment)
         self.map_statements(fragment, new_fragment)
+        self.map_domain_renames(fragment, new_fragment)
         return new_fragment
 
     def __call__(self, value, *, src_loc_at=0):
@@ -513,6 +517,15 @@ class DomainRenamer(FragmentTransformer, ValueTransformer, StatementTransformer)
                 map(self.on_statement, statements)
             )
 
+    def map_domain_renames(self, fragment, new_fragment):
+        new_fragment.domain_renames = {
+            src: self.domain_map.get(dst, dst)
+            for src, dst in fragment.domain_renames.items()
+        }
+        for src, dst in self.domain_map.items():
+            if src not in new_fragment.domain_renames:
+                new_fragment.domain_renames[src] = dst
+
     def map_memory_ports(self, fragment, new_fragment):
         super().map_memory_ports(fragment, new_fragment)
         for port in new_fragment._read_ports:
diff --git a/tests/test_hdl_ir.py b/tests/test_hdl_ir.py
index a3326e5..34d5987 100644
--- a/tests/test_hdl_ir.py
+++ b/tests/test_hdl_ir.py
@@ -8,6 +8,7 @@ from amaranth.hdl._dsl import *
 from amaranth.hdl._ir import *
 from amaranth.hdl._mem import *
 from amaranth.hdl._nir import SignalField, CombinationalCycle
+from amaranth.hdl._xfrm import *
 
 from amaranth.lib import enum, data
 
@@ -3561,3 +3562,39 @@ class CycleTestCase(FHDLTestCase):
                 r".*test_hdl_ir.py:\d+: signal a bit 0\n"
                 r"$"):
             build_netlist(Fragment.get(m, None), [])
+
+
+class DomainLookupTestCase(FHDLTestCase):
+    def test_domain_lookup(self):
+        m1 = Module()
+        m1_a = m1.domains.a = ClockDomain("a")
+        m1_b = m1.domains.b = ClockDomain("b")
+        m1_c = m1.domains.c = ClockDomain("c")
+        m2 = Module()
+        m3 = Module()
+        m3.d.sync += Print("m3")
+        m4 = Module()
+        m4.d.sync += Print("m4")
+        m4_d = m4.domains.d = ClockDomain("d")
+        m5 = Module()
+        m5.d.sync += Print("m5")
+        m5_d = m5.domains.d = ClockDomain("d")
+
+        m1.submodules.m2 = xm2 = DomainRenamer({"a": "b"})(m2)
+        m2.submodules.m3 = xm3 = DomainRenamer("a")(m3)
+        m2.submodules.m4 = xm4 = DomainRenamer("b")(m4)
+        m2.submodules.m5 = xm5 = DomainRenamer("c")(m5)
+
+        design = Fragment.get(m1, None).prepare()
+
+        self.assertIs(design.lookup_domain("a", m1), m1_a)
+        self.assertIs(design.lookup_domain("b", m1), m1_b)
+        self.assertIs(design.lookup_domain("c", m1), m1_c)
+        self.assertIs(design.lookup_domain("a", xm2), m1_b)
+        self.assertIs(design.lookup_domain("b", xm2), m1_b)
+        self.assertIs(design.lookup_domain("c", xm2), m1_c)
+        self.assertIs(design.lookup_domain("sync", xm3), m1_b)
+        self.assertIs(design.lookup_domain("sync", xm4), m1_b)
+        self.assertIs(design.lookup_domain("sync", xm5), m1_c)
+        self.assertIs(design.lookup_domain("d", xm4), m4_d)
+        self.assertIs(design.lookup_domain("d", xm5), m5_d)