I had decent results with Tensid Safety Klean, which surprised me.
I tried carbon / soot remover but the Safety Klean worked best. Most of the stuff was shifted but some of the bricks were actually fire damaged. This was after a garage fire and the area was around 15 metres square.
They'll usually send you a free sample.
I'm far from an expert in fire damage and this was a random one off call where I agreed to try and help. Guy was very happy, the fact he was not paying himself no doubt helped.