About the only advice I can give is that sandblasting is almost certainly not it.
Suggest you try local contractors - Victorian houses will be made from different bricks, depending on location, and will have suffered different depredations over the last 150-ish years depending on local industrial emissions, typical weather and so on - a house in a rural location will have led a very different life to one in a valley in the industrial heartlands.
Have any of your neighbours cleaned theirs? How did they do it?
But why do you want to clean it? Is it "dirt", or "patina"?
If you clean it, how will it look in relation to the neighbouring ones?