Blocking is the operative effect of most designations. The property is not confiscated; title does not change. It is immobilised, and the institution holding it must report it and place it in a blocked account. Dealing in blocked property without a licence is itself a violation.
Blocking travels. If a designated person’s funds pass through a correspondent account in a blocking jurisdiction, the intermediary bank is required to block them mid-payment, which is why so much evasion activity is directed at keeping payments out of the correspondent chains where that would happen.