By default forwarded calls will bypass the subscriber/call handler transfer rule and only play the greeting. This is generally how such loops are avoided. Sounds like you've intentionally configured these call handlers (or added routing rules) to perform this looping action. As you've noted however, Unity will to see this as a loop. Instead it sees each iteration as a new incoming call with no relation to any previous call. I'm not sure what you're hoping can be done further.
You might try checking what calling number shows up in the call viewer on such looping calls. If the calls are fowarded immediately (not CFNA) then the calling number after a transfer might show up as the DN of the transfering Unity port. In this case, you might be add a new routing rule that triggers off this and sends the call to the greeting of some other call handler.
Another option might be to use supervised transfers with call screening enabled. The port that answers the looped transfer will not 'accept' the call and so the transfer will be recalled.
Finally, I'm guessing you've done this to implement some form of poorman's find me - follow me feature. You might be much better served with the rules-based routing features of Personal Assisant.
-Eric
