As I understand, nomologically possible world is a world which is governed by the laws of physics of the actual world, but doesn't that kind of entail that in all nomologically possible worlds (including ours) physicalism is true? Or is the term 'laws of physics' here referring not to the results of modern physics (i.e. theory of relativity or QM), but to something broader, allowing some metaphysical claims to be true?.
The short answer is no. Physicalism is the thesis that everything is exhaustively describable and explainable in the language of fundamental physics, or in "higher-order" language, such as the language of chemistry, biology, etc. that is theoretically reducible to the language of physics. Whether physicalism is true or false is a difficult philosophical question.
Here's one thing to say though: if physicalism is true, it's probably just a contingent truth, not a necessary one. Here's why. A sentence is a contingent truth if and only if there is at least one accessible possible world in which that sentence is false. The relevant sense of possibility here is nomological possibility. So, consider all those world that have exactly the same physical laws as the actual world.
Now, suppose in one of those possible worlds there is a lonely ghost made up out of some goo that physics just cannot ever explain. We know that the ghost can't interact with any of the physical stuff--this would entail a violation of the laws of physics, but the mere fact that it couldn't interact doesn't mean it can't exist. If there is such a ghost in that world, physicalism is false. This means, that even if physicalism were true in the actual world (i.e. even if there aren't any ghosts in our world) then it is merely a contingent truth.
All this argument relies on is the idea that if one conceive of such a ghost in a world nomologically identical to ours, then it is possible that such a ghost exists. This
conceivability-possibility principle is controversial, but it isn't clear what better guide to possibility there is.