How can I make an explosion damage multiple clones, without damaging the same one twice?

Hello, I have a mine for a zombie game, and when a zombie steps on it it is supposed to damage whoever stepped on it and the surrounding zombies. Because the zombies are clones, I am unable to verify if a zombie has already been hit because a hit zombie is identical to a zombie that has not yet been hit in an explosion's radius, and if I put a debounce, the explosion will only damage the first zombie it touches and stop. Is there any way I can add a variable to a hit zombie so I can identify if it has already been hit? (I am planning to make it so the zombie can be hit again by another mine, so I would need to sort that out later on, but for now this is a big road block for me.)

Here is the code. Thank you very much.

part = script.Parent
lastHuman = nil
repeated = true
part.Touched:Connect(function()
	if repeated then
		repeated = false
		print("startExplosion")
		local Explosion = Instance.new("Explosion")
		Explosion.DestroyJointRadiusPercent = 0
		Explosion.Position = script.Parent.Position
		Explosion.BlastRadius = 20
		Explosion.BlastPressure = 20000
		Explosion.Parent = game.Workspace
		local MIN_DAMAGE = 0
		local MAX_DAMAGE = 10

		Explosion.Hit:Connect(function(hit, distance)
			local hum = hit.Parent:FindFirstChildOfClass("Humanoid")
			if hum == lastHuman then
				print(hum)
				print(lastHuman)
			end
			lastHuman = hum
			if hum then
				hum:TakeDamage((1 - distance / Explosion.BlastRadius) * (MAX_DAMAGE - MIN_DAMAGE) + MIN_DAMAGE)
				print("BLOWN UP")

			end
		end)
	end
end)'

#####Re-edited by JesseSong!