Imma give the simplest explanation I can, since JoJo abilities are kinda nuts. Basically, Tusk Act 4 is a stand that uses something called spin. Spin is the ability to manipulate the rotation of the object which can be used to to manipulate things like gravity, speed, and force (basically telling the laws of physics to go f**k themselves). Tusk is a stand that utilizes INFINITE spin, or the infinite rotation, which it can apply to an enemy to make every cell in there body spin for eternity. Tusk uses this to basically be an unstoppable force that once it hits, it wins.
Feats include:
-ripping open a barrier of infinite dimensions with it's bare hands
-the spin it applies being so unstoppable that it affects the target even after they swap bodies
-manipulating spin to the point where the gravity it creates allows it to bypass time stop
-having an attack that once it hits, can only be undone by itself
-acts on it's own accord without its user
Basically, it not only has a way to bypass infinity, but because it can act without Johnny's command once its activated, the domain expansion wouldn't affect the stands ability to attack