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There could be a lot of causes for this. He might have been stung by a bee or insect in the snout area and is rubbing to relieve the pain. He could also have an allery to a chemical (cleaning product, carpet powder) and he is rubbing to relieve the irritation.
Last but not least, dog will rub their face on the floor when they have a physical "head ache" to try to ease the pain.
If this persists, a vet visit will be needed.
Let me know if you still have questions.