recommendations for purging roaming hosts?

[#1]

We've got a number of roaming hosts, and I'm sure many aren't even valid anymore.  Are there any recommendations on how to purge out these old entries?  We do not have the network discovery option, which I'm guessing might be useful to determine which entries are no longer being utilized. 

[#2]

I assume you're referring to old DHCP records related to the clients?  Scavenging can handle that cleanup.  However, I would not take scavenging lightly as it could cause unexpected results if configured improperly, like deleting active legitimate records.  I would recommend engaging a PSE to help with scavenge configuration.  And even then, start with a small test group and slowly move from there.