CHI problem

Hi All,

I am a newbie in CHI. I have two problems.

 spec say that ,Fully Coherent Request Nodes (RN-Fs), contain coherent caches and will accept and respond to snoops.

I checked the spec, snoops are Transaction. So, what is the meaning of  will accept and respond to snoops.? Who send the snoops transaction?

In the spec 1-26, it says the coherence protocol ensures that all Requesters observe the correct data value at any given address location by enforcing that no more than one copy exists whenever a store occurs to the location. After each store to a location, other Requesters can obtain a new copy of the data for their own local cache, to permit multiple cached copies to exist.

What is the meaning of enforcing that no more than one copy exists ?

Would you explain to me  in detail?

Thanks a lot!!