from the agreement
If during the term of this Agreement you cancel Service because you move your residence to a location within a Comcast serviceable area and you reconnect to comparable Services offered by Comcast (as determined by Comcast), within 30 days of disconnection, the amount of the early termination fee will be credited upon proof of installation. If Comcast does not offer comparable Services and you activate Comcast residential Cable, Comcast High-Speed Internet or Comcast Digital Voice service within 30 days of your Service disconnection, the amount of the early termination fee will be credited upon proof of installation. To receive the credit, you must contact Comcast by calling, 1-855-487-0252 within forty-five (45) days of Service disconnection.
Since you are moving to an area where Comcast CANT provide service, I'm sure some proof of residency (utility bill) would be sufficient