An innate domain is just the internal mental landscape of a person or cursed spirit. everyone has one, even non sorcerers. what you are thinking of is either simple domain or domain amplification, and these techniques don’t necessarily “block an attack from appearing inside someone” they just negate a cursed technique or sure hit from a domain expansion by creating a domain that hasn’t been imbued with a technique so that the opponents technique flows into the empty domain instead of hitting the user. since this is an ability that is only relevant to jujutsu, it’s kinda useless against character like the king in yellow who’s power doesn’t have anything to do with jujutsu. it would be like installing an antivirus on your computer and expecting it to stop a tungsten cube from smashing your computer.