A griddle sounds like it would need libun gamur. Put it in a self clean oven on self clean, for an hour.
Is that hot enough? Self cleaning ovens heat to about 500 Celsius but incandescence only starts at about 525 Celsius. This seems like self cleaning ovens would only be good for Libbun Kal.
I never put a skillet in self cleaning oven to see if it would glow.