Yes, there is clearly a global state; first right in the contract you have its explicit, and you may distribute information about it with any data availability layer (without additional consensus), like Nostr (we also work on a dedicated DA called Storm)

dr_orlovsky

RGB consensus layer released to production

How does client-side validation work?

I vaguely remember that one critique was that true consensus is impossible because there is no global state. One asset can be sold to two other participants, and they won't know it is a double-spend unless they talk to each other. 

But later, I read somewhere you said you solved this. 

Do you know what I am referring to? If so, can you elaborate a bit?