Polyurethane is one of the most commonly used wood sealers for hardwood floors because it is durable and almost impermeable. However, this doesn't mean that it's not susceptible to the occasional scuff left from a shoe -- black-soled dress shoes are the most notorious culprit of unsightly scuffs. Since polyurethane is so durable, you won't have to worry about damaging the floor when trying to remove scuff marks, especially since the most common methods don't require abrasive scrubbers or heavy-duty solvents.
Clean up the area around the scuffs with a sponge or cloth and a mild detergent formulated for use on wood floors. Since you may have to rub the scuffs vigorously, you must remove dirt, grit or any other abrasive debris that may scratch the surface of your wood.
Rinse the floor with a damp cloth and wipe the floor dry with a fresh cloth or paper towel. Buff the scuff mark away with a tennis ball. You may also rub the scuff away with your foot while wearing a clean sock.
Sprinkle a small amount of baking soda directly on the scuff. Buff the affected area with a damp cloth until the scuff disappears. This method is best for heavily scuffed areas.