Cast Iron Casualty

Mexican food is a favorite at our house, but I have never been able to make it quite as good as the restaurants. After looking online, I discovered that the "secret" is very high heat and resisting the urge to stir, stir, stir.
I was very pleased with the way our fajitas turned out... but my poor cast iron pan didn't take to the high heat and the marinade, oil, etc. mixture very well.

I've boiled H2O, scraped, chiseled, and scrubbed... but my pan is still not smooth and velvety like it was before. So - it looks like it's time for the die grinder! Any other suggestions would be welcome... at this point I'm afraid my poor pan may never be the same!!