Replicating users to the global catalog

I am a software developer so I don't have very much experience with Active Directory and setting up domain controllers, etc... so I am currently just trying to set up the simplest network possible to do one thing.  All I want to be able to do is have 2 domains, A and B (in the same forest).  Then I want to be able to get users replicated from domain B into the global catalog.   That is all I need to achieve for now so I can do my testing.

I have a simple network set up: domain A and domain B.  Domain A was the first domain created in the forest, so by default he stores the global catalog.  I then added a second domain to the forest domain B.  I created a user "testuser" in domain B.  I then created a universal group "testgroup" in domain A and added "testuser" from domain B to "testgroup".  I now assume that "testuser" should get replicated to the global catalog since he is a member of a universal group.  The user does not get replicated.  I have gone into "Sites and Services" and performed a "Replicate Now" from domain B's server.  It states that the replication completed successfully, but I go and look in the global catalog and "testuser" is not there.  By the way, I am examining the contents of the global catalog using the ADSI Edit tool.  
Also, I have checked the replication topology using "Sites and Services", and it always checks out ok.  It seems like this should be something easy and pretty basic to do, I am probably just missing something simple.