How do I Find which GUP Serves Which SEP Clients?

I created location-based policies designating a machine at each remote office as a Group Update Provider, and I see updates being downloaded to the SharedContent folders since then.  I can verify the machines are GUPs by searching clients for "Group Update Provider = TRUE".  

But how do I verify that a client is getting updates from a GUP, and how do I know which GUP they are contacting?