basically, understand that you cannot tcp reset all signatures, because not all signatures are tcp based signatures. Also, it typically does not help to tcp reset a tcp port scan because of the nature of port scans. Tcp resets are good for connection oritented alarms or string match alarms that you would create. i.e. telnet or ftp based string matches or even smtp.
Shunning would be better suited for your port scans, icmp attacks, and whatever else would be a "reconnaissance" type of probe or scan where someone is looking for something to attack on your network.
hope this helps.
