The word used is erets Strong 776. Brown Driver Briggs (see the Strong link) lists the use of the word in Genesis 41:54 as - unusually, so early in scripture - the plural :
and the dearth was in all lands; but in all the land of Egypt there was bread. [KJV]
BDB comments that the use, generally, of the plural is a matter of a contrast to Canaan.
I would suggest that here in Genesis 41:57 :
And all countries came into Egypt to Joseph for to buy corn; because that the famine was so sore in all lands, [KJV]
it is, similarly, a contrast but a contrast of all the lands as opposed to the land of Egypt itself.
As with contrasts, the word may not be meant as a true totality of concept but is only used as a contrast of concepts.
The whole known earth - as known to the most settled area of the globe at that time - was in famine. Distant, almost unknown, regions - where little would be heard except the odd tale of far flung, never visited, regions where nations may or may not have settled permanently are not, necessarily, being included, as such.
I would suggest that it is a contrast of dearth in the lands, within the compass of what was generally known, being compared to the prosperity of the land of Egypt, which is in view.