Its a good question, you are required to co-operate with the authorities in the lawful execution of their job. The term 'lawful' is, of course, subject to legal interpretation.
Police have arrested people for filming them arresting others, typically the scenario is "They ask the person filming to stop while they are doing their job, person doesn't, they arrest them for interfering with an officer." (sister-in-law is a public defender, I get to hear all the excuses). So far the California lower courts are still fumbling around this issue. I expect it to make it to the ninth circuit sometime later this year or early next year.
The question of "Can you make a house that the police can't search without your co-operation?" is a good one, and I'll ask my lawyer friends if that approach has been taken yet. Generally a subpoena is the court ordering you to co-operate and generally you must (or be held in contempt of court).
So I expect such cases would go "give us your hard drive" followed by "give us the key", followed by a refusal, followed by a subpoena, followed by another refusal, followed by being in jail for contempt.
If you did shred your key so that you literally cannot decrypt the drive, then I would expect you to spend a few days in jail (so that the prosecutor could prove to themselves you are serious) and then they would return your drive after re-formatting it. How they would justify that I do not know but I know that they would try.