Dominated: The creature can’t take actions voluntarily. Instead, the dominator chooses a single action for the creature to take on the creature’s turn: a standard, a move, a minor, or a free action. The only powers and other game features that the dominator can make the creature use are ones that can be used at will, such as at-will powers. For example, anything that is limited to being used only once per encounter or once per day does not qualify.
Situation: a dominated creature is forced to attack itself with an attack that also has a Push effect. Can the creature be pushed in any direction, or can a push originated from the target's square not go in any direction?
The compendium provides two different definitions for Push:
Push: When you push a creature, each square you move it must place it farther away from you. (from the entry on Push)
Push: Pushing a target means that each square of the forced movement must move the target farther away from the creature or effect that is pushing it. (from the entry on Forced Movement)
This seems to suggest that the push can go in any direction, because any direction is farther away from the origin square; then again, if the target is the creature that is pushing it, then it cannot move farther away from itself.
Here's some examples of monsters with push powers:
Spell Weaver Collector
Repulsing Touch (minor, at-will) Force
+11 vs Reflex; 2d6+4 force damage, and push the target 5 squares.
Longsword (standard, at-will) Force, Weapon
+13 vs Fortitude; 1d6+5 damage, plus 1d6 force damage and push 3.
Forceful Dagger (standard, at-will) Force, Weapon
+33 vs AC; 4d4+10 force damage, and push the target 1 square.