Given that no matter to speak of ...
... is or has been manufactured in our local galaxy, and given that the portion other than hydrogen was pretty much all manufactured in stars, and is pretty evenly distributed amongst the hydrogen, I'd say that ALL of the matter in the Milky Way came from other galaxies. Lex parsimoniae[1] & all that.
[1] Occam's razor, for the illiterate amongst all y'all.
Biting the hand that feeds IT
