Is there any lore-wise reason that Domination wouldn't work on them?
Perhaps Scions unit class should be reclassified entirely.
For instance, when I made the unfortunate discovery that undead slaying doesn't effect them.
As for Domination Versus The Scions, perhaps just a 30% save against it (on top of the normal 20% to fail) would be reasonable. Especially since the loss of Domination means you need to rebuy it with your next promotion to regain it. It would make dominating Scion units a tactical risk (Can I afford a 50% chance to lose this).
So Undead Slaying not working on Scions is a bug but Domination is not?
I believe Domination can only be resisted if the unit has magic resistance. Otherwise, I don't think there's any natural unit resistance.
hard dominate someone who's head is in a jar.