Depending on the type of stone from which the front doorstep was made, there were a variety of methods of cleaning. A perfectly clean doorstep was paramount in the lives of most town-dwelling women. Happily, fashions have changed!
In the south of England most steps were of Bath or Portland stone - a form of limestone. They were cleaned with a "holystone" and then whitened. I cannot remember the name of the whitening agent (although I sold them when working in my parent@s shop in the '50's) but it was a block the size of a large bar of soap and was used with water. I berlieve the holystone was a block of pumice stone, similar to that used when scrubbing the decks of ships (of for removing hard skin from your feet).
Colyn.