You don't need reserves for interbank settlement either. That's actually a centralised optimisation to reduce collateral requirements. At root if you transfer

You don't need reserves for interbank settlement either. That's actually a centralised optimisation to reduce collateral requirements. At root if you transfer your deposit to another bank that target bank becomes the depositor in the source bank. Or the transfer can't happen. Banks then shuffle those deposits they have take on around until they are happy with the risk. That's interbank clearing.