You are confused there are settlement accounts that are used to settle the transfers. So if you are doing a transfer from Chase account to CIBC FirstCaribbean International Bank account (for simplicity's sake we will assume that CIBC FirstCaribbean has a direct relationship with Chase) the appropriate debit and credit will be reflected in appropriate nostro and vostro settlement accounts. The SWIFT message is just a mechanism to exchange information but the actual money movement happens between settlement accounts.