If you want to clear out a specific variable, you can just set it to null and it will no longer contain the cached data:
$Cache:Datalist = $null
If you want to completely remove the record from the cache (including the key), you can clear the item from the cache directly. It won’t really save any more memory unless you have millions of items in the cache.
[UniversalDashboard.Execution.GlobalCachedVariableProvider]::Cache.Remove("datalist")
If you want to completely remove everything stored in the cache, then use Clear().
[UniversalDashboard.Execution.GlobalCachedVariableProvider]::Cache.Clear()