Synchronization lock across AppDomains

I have a multi threading scenario where i need to synchronize calls over a
routine. For that purpose i use a static generic list (synchronized). The code
need to be synchronized reside in a separate assembly. I access it from win
service context (thread pool) and web server context. In each context
synchronization works fine, but this is not true across both contexts. I did a
research and i find out that static state is not shared across AppDomains.

So my QUESTION is: How can i share state for locking purposes across the
AppDomains most effectively and can you point me to some reference code?

Thank you in advance.

Use a named mutux - it can be used across process, too. 

http://msdn2.microsoft.com/en-us/library/system.threading.mutex.aspx