This works fairly well for ours; Sprinkle some common table salt on a damp cotton cloth (barely damp, not wet) and with the iron on the cotton setting but not steam, iron over the salt covered cloth until the marks disappear... voila!
If it's just scorching and not rust, it should work. Be sure to clean the sole plate with a good clean cloth afterwards to remove any remaining salt...
place several spoonsful of salt on a soft cloth. Lay it on the ironing board. Turn the iron on to the cotton setting (no steam!) and iron over the salt until the scorch marks disappear. When the iron cools, wipe the sole plate with a damp cloth.