By your role-play, you are personifying a Rheinland battleship captain. His orders are to guard Rheinland. Your ZOI = Rheinland's interest. If the ZOI doesn't cover the system you're hunting for Nomads in, then that is not part of your interest and you are acting contrary to orders. It is not against the rules, but if the Rheinland Military High Command find out you moved a battleship belonging to the Fatherland there, they are going to be angry.
It is different if you are a trader. A trader's ZOI isn't much different, but they actually have some business outside the House -- which they must leave in order to trade with other Houses. They just can't shoot stuff there except in self-defense, because that's the job of the local law enforcement.
Of course, you can say that you are fighting the Nomad threat outside of Rheinland. But it is not your role, unless you are ordered so by the RM HC. There are local factions (Order and Core) whose job it is. If you want to hunt for Nomads, make a character in one of those factions. If you want to sell them as well, make a Core character, because the Order's goal is to destroy the Nomads, and the Core's to use their technology and even sell it so they could fund their operations.
