The halacha is you can only build a city of refuge in Israel. What if someone killed by accident outside of Israel. Can the relative of the guy who was killed go after and try to kill the murderer who killed by accident?
Sifri states that the Cities of Refuge also serve people who live outside of the Land of Israel. According to Kesef Mishneh's first explanation, that means exactly what it sounds like: an accidental murderer from another country would have to run away to the nearest City of Refuge in Israel (or Transjordan), and until he does so he would be subject to attack by the goel hadam (the nearest relative of the victim).