I've run into the term "hegemonic discourse" a few times in Marxist writing in the last week. Here's what I think is going on with this one:
Marx himself had tried to make his arguments using logic and facts. But what became of Marxism after his death, in terms of logic and facts, was not pretty. The logic of Marxism was dismantled by the rise of the marginalist school of economics. The supposed historic dialectic sequences were shown, by historical research, not to have played out in the way Marx thought they had. And capitalism's development did not reflect Marks's predictions as to what would take place.
What to do? Well, one could say "Karl Marx was a very bright guy, but clearly he went wrong somewhere." But by this point Marxism had become a religion, and religions are not given up easily. So if the logic and facts were against Marx, then they themselves must be the problem! So someone using logic and facts to show that Marxism is fundamentally mistaken is engaged in "hegemonic discourse," and his logic and his facts are themselves the tools of oppression.
Now your theory is irrefutable, as the only known ways to refute a theory are logic and facts! Whew, that was a close call.