Did you check if the connection was up between the domains? Regardless of the state of the connection, the domain gateway in domain 1 will advertise TOLOWER and if no connection is up when the service is called, the domain gateway will try to establish the connection. If the connection succeeds, then the call will complete, otherwise the call will fail, but the service will still be advertised. On domain 2, TOUPPER should only be advertised by the domain gateway if the connection is up. You can use dmadmin to check the state of the connections, as well as manually try to connect or disconnect the connections.
Oracle Tuxedo Chief Architect