Currencies do not necessarily have to have a total order (you don't like that, do you) or hierarchy.
Bingo!
National currencies were/are the citizen's unit-of-account because it is very costly store your cash flow in a unit-of-account which is not the predominant unit-of-exchange.
Now that we are transitioning to B2C and P2P (C2C) globalized commerce, we need in some areas (especially intangible Internet commerce) a globalized unit-of-account and exchange.
Read that second sentence again and understand the profound implications. The coming moat is no longer national boundaries but tangible versus intangible (Industrial Age versus Knowledge Age) commerce. Also make sure you read my essay in the Economic Devastation thread.
I fully agree that commercially-knit-together communities do not need necessarily to be *geographically* close (even though for most of commerce, that is still the case: the plumber, the groceries, the bread, the car repair, the doctor, the dentist, the leisure.... much commerce remains local). But usually these communities are not very big even if spread out. Maybe I trade international post stamps, but the exchanging of post stamps is not related to the community of violins trading internationally.
I very rarely buy stuff abroad directly. It happens. Most of the time, I use products that have of course partly foreign origin, and most of the time when I buy "foreign made" stuff, I use a local retailer. I very rarely buy my oranges directly in South Africa. I buy oranges in a local grocery shop, who got them there from Morocco or South Africa. But that's not my problem. I pay the grocery shop holder in the local currency. He probably needs to exchange money to buy the oranges. It is his business.