How can I delete all inactive widgets?

I want to cleanup all inactive widgets. I tried following snippet as suggested by this answer Script to remove all inactive widgets?.

$sidebars_widgets = get_option( 'sidebars_widgets' );
$sidebars_widgets['wp_inactive_widgets'] = array();
update_option( 'sidebars_widgets', $sidebars_widgets );

I also tried deleting option sidebars_widgets directly from the options table.

But after page is refreshed, old value is restored with all inactive widgets. How can I remove all those inactive widgets at once? Thanks in advance.

You should do it with after_setup_theme action:

function remove_inactive_widgets() {
     $sidebars_widgets = get_option( 'sidebars_widgets' );
     $sidebars_widgets['wp_inactive_widgets'] = array();
     update_option( 'sidebars_widgets', $sidebars_widgets );
}
add_action( 'after_setup_theme', 'remove_inactive_widgets' );