This is a great question and I am also curious about the answer. I always assumed it was an import from logic, e.g., range and domain. I have written a bit about the further appropriation from computer science by the DoD in defining the "cyber domain" which first appears in 2000 and then takes off. As late as 1999 military writers would talk loosely about an "information arena" or "commons" something like that, but "domain" takes off later. I read this as largely a bureaucratic bid for legitimacy, defining "cyber" as coequal with land, sea, air, and space, with the USAF attempting to lay claim to three of these (air, space, cyber). Legal discussions of domain are much older, usually used to distinguish territorial waters from high seas, which is interesting in that the "cyber domain" would in that sense be just the opposite of a "cyber commons", but if you are a global hegemon perhaps you can pretend to dominate a global commons. I have a suspicion that the logical computer science usage of domain thus made it really attractive to the military to play off of the meaning "to dominate" not just an arena or bounded conceptual area.