I don't know enough about Visa's design to comment authoritatively - but my working assumption is payments from issuing to acquiring banks in-country are done net and through visa - i.e. one net payment per issuer into visa and one net payment out to acquirer. e.g. see the last page of this doc: https://usa.visa.com/download/merchants/visa-core-principles...
What isn't obvious to me is what happens in international scenarios - you ask a great question.
What isn't obvious to me is what happens in international scenarios - you ask a great question.
[EDIT] - Actually - here's your answer.... See section 2.3.3 of this doc: http://www.bis.org/publ/cpss53p16.pdf