That doesn’t make a difference. A transfer from a bank account held by one bank to an account held by another will always and inevitably result in a transaction between the two banks; assets of the sending bank decrease (but, conversely, its liabilities also decrease, because they deduct the amount sent from the sender’s account, and that account is a liability of the bank), and correspondingly, assets of the receiving bank also decrease (but, conversely, its liabilities also increase because the same amount is credited to the recipient’s account, which is a liability of the bank). At the level of the two banks, the interbank transaction is, in fact, a flow of assets from one bank to another, which is accompanied by changes to the account balances held by customers with the bank. In the case of a transaction done on the bank’s own behalf (e.g. because bank A bought securities from bank B), it’s exactly the same, only that the corresponding changes in customers’ balances don’t take place.