It's a question I get asked a lot. Not so much by mortals but by other Divines. Some have demesnes obvious and contained: Elassa, Anassa, Neneria & Kavaa all restrain themselves to tight-knit, highly-literal, interpretations of what Magic, Sorcery, Death & Health are. Others, like Kassandora and Fortia, try to claim the world with their demesne. Both could make even a drop of rain somehow fall under their purview.
Of course, both are wrong. They are wrong not because they are wrong, but because they simply don't have perspective. Only demesnes such as Arascus' Pride or Galrond's Gluttony, which are intrinsic to humanity, can even lay claim to omnipresence. And in that, then it is mine which is at the forefront. In this regard, it is irrelevant to apply materialistic descriptions to my demesne.