Old Domain Listed in Dropdown Dialog

I have a test lab setup and I am testing migrating from an NT 4 domain to a 2K domain. When I join the PC to the new domain and bring to old domain controller offline, I can still see the old domain name in the dropdown list. Is there any way to remove this? I have searched the registry for the Old Domain Name and it does not find it, my guess is that is in hex or something. Any help in getting rid of this would help, since I don’t want my users to have to deal with this problem.