There are two forms of liability with options. The margin and the actual final settlement. Every day the options are evaluated to see their value. As the options fluctuate in value one counterparty will need to post more collateral and the other side will receive the collateral. In the case of OTC options the collateral may go to a neutral 3rd party. In the case of listed you are going to deliver collateral to the OTC.
In all of the above cases you are not delivering reserves. You are delivering bonds, bills, maybe gold, certain stocks in the case of certain collateral agreements.
For final settlement, you get your collateral back and then use SWIFT to sent the actual money. In that case you are sending actual reserves. Then, as mentioned above, the reserves are entirely fungible.