You'd tax global profit based on the local revenue fraction. So if the corporation has global profits of 1M and the revenue is 90% in country A and 10% in count

You'd tax global profit based on the local revenue fraction. So if the corporation has global profits of 1M and the revenue is 90% in country A and 10% in country B, then country A taxes 0.9M of profit and country B taxes 0.1M of profit and neither has to care where the corporation is located 'for tax purposes'.