If UserA requests a resource from DomainB such as IIS server named ServerB, ServerB will contact Domain Controller of DomainA. Your trace is expected and technical explanation of this behaviour is detailed in the following link:

Ref: https://learn.microsoft.com/en-us/openspecs/windows_protocols/ms-nrpc/70697480-f285-4836-9ca7-7bb52f18c6af