HELP! Does anyone know how to clean heavily stained terrazzo flooring?

The flooring was laid down on a slab foundation and was then covered with carpeting. Later the carpet was removed and the flooring is heavily stained with pet stains and general grime from heavy traffic as a result of the carpet, ie, anything that was spilled on the carpet soaked into the flooring. We have tried baking soda, peroxide, every commercial cleaner that we could think of and nothing will even budge the staining especially the areas of pet stains. The entire floor is covered in a grey haze. Any help or resource would be appreciated. Thanks!