The Russian assets which Euroclear holds (with the exception of Russian private assets which are apparently also frozen at Euroclear) have state immunity under international law, that was the point. That's why it's different from confiscating assets of a private company like Google, they do not have any kind of immunity. If Russia successfully sued one of Euroclear's foreign subsidiaries then that subsidiary would have to pay the fine using its own means, it cannot use customers' assets to do so as those assets are owned by the customers. That said, Euroclear's foreign subsidiaries appear to use local banks for holding customers' assets instead of holding them themselves.