I agree with Richard that LISTSERV should always check the local list
before sending the request to another server.  It shouldn't cost too much
to make that check.
 
There is a way, however to get that person who is at the "WRONG" server.
Use the "GLOBAL" parameter on the delete command.  This will cause the
"RIGHT" server to receive the command, and if the person is not subscribed
locally, to forward the command to all other peer servers.  One of them
will be the server where the user is subscribed and he will be deleted.
This has been described as the "IGOR" option. "Get him, Igor"
"Yeeesss Maaaaster"
 
     Tell listserv at EB0UB011 DEL MAILBOOK FRED@WHATEVER (GLOBAL
 
Harold