Gas stations have been successfully sued under such laws. So clearly, there's some flexibility when it comes to the definition of dominant.

i don't know the case behind this example, but i can imagine that if a small city only has a few gas stations, even just one undercutting all the others, forcing them to close would be a form of domination.

so basically (and i am just guessing here) a company becomes dominant the moment its competitors start going out of business because of this companies predatory pricing.