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!