From a chemistry point of few, getting carbon build up to react with hydrogen would create reverse the processes that left the deposits (i.e. hydrocarbons, such as fuel and oils returned back into hydrocarbons). In the simplest form, it would react back into Methane but this theory is flawed as you'd need a hell of a lot of excessive energy available to force the carbon molecules to break apart and then react with the hydrogen.
And methane is highly reactive so would almost instantly react again with any oxygen, which created water and carbon dioxide and, you guessed it, soot. Which, funny old thing, is a carbon build up!