You can throw an event (may be your custom event) when the message is recieved and the another process may have a event start point using which it would be invoked, when it catches this event.
For continuos monitoring, you can create a loop using Wait Point
See below links :
http://help.adobe.com/en_US/livecycle/10.0/WorkbenchHelp/WS92d06802c76abadb-1cc35bda128261a20dd-7f4f...
http://help.adobe.com/en_US/livecycle/9.0/samples/ServiceUsageSampleEventCorrelation.html
Hope this helps.
Thanks,
Wasil