From the CLI (Command Line Interpreter) Guide
-purge{-filenames [host_1 [host_n...]] [-force]
so, no commas, just a 'space' between each hostname
The -filenames option removes all obsolete file names (file names without any file versions)
for a specific or all clients from the CDB. This option requires exclusive access to the database.
Data Protector does not start the process for removing obsolete file names if the number of
obsolete file names does not exceed a specific threshold. When starting removal for the whole
cell, use the -force option to enable the removal in cases when there are fewer than 5000000
obsolete file names in the IDB. When starting removal for the specified clients, use the
-force option to enable the removal also for clients which have fewer than 1000000 obsolete file
names in the IDB.
By the way, the CLI Guide can be found from the gUI by clicking Help -> Guides