In VLF-ONE applications the virtual clipboard contents persist in the web browser's local storage.
Clearing the web browser local storage will clear all clipboards.
Additionally, the shipped demonstration left slider DF_SLIDLB has this option:
Which executes this code:
#avFrameworkManager.uClearUserVirtualClipboard Signalchange(True)
#avFrameworkManager.uClearSystemVirtualClipboard Signalchange(True)
to clear the user and system clipboards.