Finding out where ssh X11 sessions are forwarded to
 

I want to be able to SSH to a machine, and have the .profile take actions based on where the $DISPLAY goes (not who the user is).

Problem is, the DISPLAY variable is masked from the host, because ssh does some forwarding. echo $DISPLAY shows something like x.x.x.x:15.0 and the IP address works out to something other than where the actual display is. So how can one find out where the $DISPLAY is being forwarded to?