I've used a heat gun - think hair drier on steriods - to help soften tar and asphalt. This does make it easier to scrape off whatever it may be on. I have also used my 4 1/2 inch grinder with a 3 1/2 inch heavy duty rope wire cup on it to cut through the thicker layers. I would not use a torch as the tar could catch fire
- at the very least it would smoke reeeaaally bad!