Banks have multiple ledgers to keep track of who owns what and where it all came from. They also use ancient fortran/cobol written IBM owned software to manage all bank to bank transactions, which is the barrier for entry.

Blockchain is literally a multiple ledger system. That is all it is. The protocol to send and recieve funds is open for all.

Locally stored BTC is when you're the bank. For all the good and bad that comes with it.