This is an old thread, but here is the solution for using a UNC path for anyone searching and finding this:
exec xp_cmdshell 'PushD "\\UNCPath" &&(forfiles /m FileName*.* /d -180 /c "cmd /c del @FILE") & PopD'
\\UNCPath is the complete UNC Path of the directory you are searching for
FileName*.* is the file name you are searching for. Use Search arguments such as *
-180 is the number of days to keep
Francis
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