GPOs and subnets

I have 3 subnets connected by a frame relay WAN link and only one DC in the main office.
TO combat the bugbear virus I created a GPO that will run a script on logon that will copy the removal tool, run the tool and copy the log file to a central location so I can see which computers are infected.

But on the external sites the script is not running. If there some rule about a GPO only running only machines on the same subnet as the domain controller ?