I'm not totally sure that i've understood your point, but i think you mean that you've made a healing shockwave? U don't need triggers for this, just make shockwave or carrion swarm negative amounts.
Ofcoarse, if you wanted a specal effect like a bigger model or something then you would need to use the dummy unit thingie. I think you've made something like every 0.10 seconds of gametime move unit blablabla? And in this trigger you pick all units nearby the dummy unit and heal them, correct?
If that's the case, the answer is simple. Use a unit group! when picking all units around the dummy unit add the condition (matching) unit is in (unit group) equal to false.
After the unit have been healed, add them to the unit group. When the spell is complete, remove all units from the unit group.
Oh, and i have a thing that makes me say a big nono when it comes to custom unit values, since if you want it to work correctly u can only use it for one thing per map.
I prefer unit groups, they have infinite possibilities! (well almost)
Hope i helped ya!
