If you are running a CPL or $ per sign up program, then you can set up a geo-targeting filter. You can do this by either including the regions you want to track and pay commission for or excluding certain territories.
Go to "Campaign - Program Terms" and Geo-Targeting option will be there. Select the countries to include or exclude. Make sure to include any special terms and conditions around this in your program description, for example, "This campaign pays our on Australian traffic only."