Demesne, or domain, is a sub-dimension inside 'our' universe with a strong ideological affinity.
Demesnes can be found everywhere in the universe, and range from the impossibly vast to surprisingly tiny. The area of space around the Demiurge wherein Earth happens to be, is particularly densely packed with these itinerant realms. Most of them have occupants from both the Elder Gods and the younger New Gods. The span of the Demiurge reaches across many star sectors, and some of the demesnes are thusly quite far-flung from others.
As most of the New Gods are creatures of energy and will rather than matter, their spirits are attuned to the energy of their home planes. Demesnes and their rules range from the small-scale (petty sorcerers with a few acres of personal space) to near-infinite Hell and The Dreaming. The inherent power of a demesne is directly correlated to its size and the number of inhabitants, in terms of both gods and souls.