Scratches can be very difficult. If they aren't too deep, then you might try a steel brush or sand paper and slowly try to sand them out. Do it first on a small part to see that it looks ok. You could end up with an unnatural look that would disappoint you.
There really is nothing to do if the scratches are too deep. Stone will weather over time and then they won't be too noticeable, but that will take a few years.
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