You might be able to get away with your specific case
I am not a lawyer, and I'm not qualified to give legal advice. However, reading the OGL, it looks like you're in a gray area:
7.Use of Product Identity: You agree not to Use any Product Identity, including as an indication as to compatibility, except as expressly licensed in another, independent Agreement with the owner of each element of that Product Identity. You agree not to indicate compatibility or co-adaptability with any Trademark or Registered Trademark in conjunction with a work containing Open Game Content except as expressly licensed in another, independent Agreement with the owner of such Trademark or Registered Trademark.
What is product identity? A huge list of things:
"Product Identity" means product and product line names, logos and identifying marks including trade dress; artifacts; creatures characters; stories, storylines, plots, thematic elements, dialogue, incidents, language, artwork, symbols, designs, depictions, likenesses, formats, poses, concepts, themes and graphic, photographic and other visual or audio representations; names and descriptions of characters, spells, enchantments, personalities, teams, personas, likenesses and special abilities; places, locations, environments, creatures, equipment, magical or supernatural abilities or effects, logos, symbols, or graphic designs;
A divine domain could arguably be one or more of the things described above (thematic elements? concepts? special abilities?), especially if you explicitly tie it to the PHB.
However, divine domains are not a uniquely D&D thing. You can probably say that Loki's domain is Trickery and Thor's domain is Thunder without violating copyright, for example. Thus, careful wording might help you dodge your issue. Then again, I'm not a lawyer.