bool Associative Array Synchronized

[Etienne]

I'd like to "cowboy it" on an AA that looks like this:
__gshared bool[string] m_mutex;

I think it'll be much faster for my code because this AA could need to 
be checked and switched possibly millions of times per second and I 
wouldn't want to slow it down with a mutex protecting it.

I'm thinking the bool would be synchronized at the hardware level 
anyway, since it's just a bit being flipped or returned. Am I right to 
assume this and (maybe an assembly guru can answer) it safe to use?

Thanks