The oven cleaner cycle was a good idea for the resin - I'm not sure what else would have worked - but it won't do anything more to what is already basically a form of graphite (which has an extremely high melting point, and a fairly high ignition point).
You need to oxidize the carbon. That would be bleach or hydrogen peroxide + time and, if you can, sunlight (so set it outside to soak for a bit with this stuff). This is gonna take several hours, and it may take more than one round to get all of the scorching off, but it will come off completely if you are patient and persistent enough.
EDIT: Though the method I've described is what I've done in the past, I read that heat + baking soda + water (+ vigorous scrubbing) can also work.