Can I use my ZVV travelcard for journeys that are partly outside the ZVV territory?

For trips outside the ZVV territory the ZVV zone tickets are only valid until/from the last stop in the specified zones according to the timetable.

As an example: You have a ZVV NetworkPass for all zones and wish to travel from Zurich to Chur. In this case, you will buy the SBB ticket from your train's last stop within the tarif area of the ZVV, in this case from Pfäffikon (SZ) to Chur. If you were to use a train without a stop between Zurich main station and Chur, you would need to buy an SBB ticket from Zurich main station to Chur.