And look at the definition of "unavailable as a witness" under California Evidence Code section 240.A subpoena issued by a state court is valid only within its geographic boundaries. Consequently, a subpoena issued in a state within which an action is pending cannot be used or served in another state to compel a non‑party witness who resides or works in the foreign state to give testimony or produce records.
The principle is equally applicable to sovreign countries as it is to different states within the United States. If you want to know more, you might do your own research or go down to your country law library and ask the librarian there.
From an article published on May 6, 2010:
So there you have it. The hearing was this year, not in 1977, the prosecutors actively opposed unsealing the transcript, and the blogger you quoted didn't check his facts very well.Prosecutors are asking a Los Angeles judge to reject a request by Roman Polanski’s attorneys to unseal transcripts of closed-door testimony in the case.
Polanski’s attorneys want a judge to unseal testimony earlier this year by the original prosecutor handling the case, Roger Gunson. They say it will help their efforts to fight Polanksi’s extradition from Switzerland, where he remains on house arrest.
Prosecutors on Thursday argued in a court filing that Polanski’s motion should be rejected because he remains a fugitive.