Jordi, Miljenko, this was exactly what I meant by having a more detailed discussion ;)
In my opinion it all comes down to the requirement you have for a particular case. I can see that both of you have similar situations to deal with but I can find number of examples where the default behavior (signal all process instances regardless of the session) can be beneficial. For instance, bank would like to notify all customers that are currently in loan process that terms and conditions of the loan has changed, so if every customer that is tring to get a loan, has started a process and by that mean has its own session to controll the process system would need to find all sessions and then signal it one by one which would not be so nice.
But as already could be seen the other side of that case is also quite common. Question is on what level shat that be configured? And if variable scopes are not useful here? I mean perhaps by inserting process variables instead of facts would make sense or not? It could be acceptable if only the process is going to use that piece of data.
Cheers