How can the caller's process be identified in

Question

I have an ATL service running as an out-of-proc server that has several COM classes that the clients are expected to be using. Because of a change in requirements, I need to be able to identify which process owns which instances of the objects. I'm trying to use some of the COM functions to find out this information but I can't find the right ones. CoGetCallContext only returns information about the user who called the method, not which process it came from. Same with CoQueryClientBlanket. What function can I use to find out this information?