Please, Please do not use heat to remove this stain. The comment poultice will work but the heat. A few years ago MB said that heat will work and we tested the claim. Here is a video of what took place when we use heat. I hope this helps.

heat has different effects on different stone thats why you have to know your stone and what will and wont work

The stone tested was the most common stone at the time for sings of the big green.
It is best to stay away from methods that cause problems. In other stones the effects may not show up in 48 hours but who knows what happens 5 years down the road.