Just found this little vbscript:
'Author: Lair360
'Version: 16.6a
'Revision: 36 Build 16
'--------------------------------------------
On Error Resume Next 'This line will cancel the error and direct to the info.
Dim objShell 'This will maintain memory usage when "WS.script.Shell" is activated.
set objShell = createobject("wscript.shell")
objShell.run("%comspec% /k c: & ipconfig /flushdns")
'Results are given and cmd command-line has exit.
WScript.Quit
'End of VBScript command
'-------------------------------------------
WScript.Echo "DNS Caches are flushed!"
objShell = Nothing
'VBScript Ends
You can launch it on your workstations using GFI network scanner for example.