In their Curious Objects exhibition Cambridge University Library's English Globe (of 1585-ish) came with an annual maintenance bill which included its scouring, which seems to have involved reapplication of new varnish. Is this practice (in general, among owners of globes) an etymological origin for the corresponding metaphorical phrase scouring the globe/earth, or a coincidence?
When I hear the term 'scour', I think first of scrubbing (eg 'scouring pads'). The German 'scheuern' is related and also means scrub. To scour a globe likely included scrubbing it before varnishing.
To 'scour the globe' is something like to 'comb the globe', both implying thorough inspection or treatment.
I imagine the semantic similarity between the processes of scrubbing and of searching meticulously is the origin of the phrase 'to scour the globe', just like 'to comb the globe'.
I don't think we can disprove your proposed etymology, but I think mine is more likely.