The infrastructure master ' s job is to periodically compare its domain ' s phantom records (placeholder stubs created for objects, such as group members, referenced from other domains) against the full, current data held by a global catalog, and to update any phantom found to be stale, which is how cross-domain object references stay current; this comparison only produces useful updates when the infrastructure master itself is NOT a global catalog server, because a domain controller that is also a global catalog already holds a complete, up-to-date replica of every object in the forest and therefore never perceives any of its own phantoms as stale, silently skipping updates that a non-GC infrastructure master would have caught and propagated. In this forest, DC1 holds the infrastructure master role for contoso.com and is also a global catalog server, which is precisely the unsupported combination (permitted only in a single-domain forest or when every DC in the domain is a GC, neither of which applies here) that causes exactly the symptom described: cross-domain references in contoso.com failing to update for branch.contoso.com objects. Transferring the infrastructure master role for contoso.com from DC1 to DC2, which is not a global catalog server, resolves the issue with a single, minimal role transfer. Transferring the PDC emulator, schema master, or domain naming master roles would not affect phantom/cross-domain reference updates at all, and DC4 already correctly holds branch.contoso.com ' s infrastructure master role on a non-GC server.