remove_user_from_blog( int $user_id, int $blog_id = '', string $reassign = '' )

function remove_user_from_blog($user_id, $blog_id = '', $reassign = '') {
	global $wpdb;
	switch_to_blog($blog_id);
	$user_id = (int) $user_id;
	/**
	 * Fires before a user is removed from a site.
	 *
	 * @since WP-MU (3.0.0)
	 *
	 * @param int $user_id User ID.
	 * @param int $blog_id Blog ID.
	 */
	do_action( 'remove_user_from_blog', $user_id, $blog_id );

	// If being removed from the primary blog, set a new primary if the user is assigned
	// to multiple blogs.
	$primary_blog = get_user_meta($user_id, 'primary_blog', true);
	if ( $primary_blog == $blog_id ) {
		$new_id = '';
		$new_domain = '';
		$blogs = get_blogs_of_user($user_id);
		foreach ( (array) $blogs as $blog ) {
			if ( $blog->userblog_id == $blog_id )
				continue;
			$new_id = $blog->userblog_id;
			$new_domain = $blog->domain;
			break;
		}

		update_user_meta($user_id, 'primary_blog', $new_id);
		update_user_meta($user_id, 'source_domain', $new_domain);
	}

	// wp_revoke_user($user_id);
	$user = get_userdata( $user_id );
	if ( ! $user ) {
		restore_current_blog();
		return new WP_Error('user_does_not_exist', __('That user does not exist.'));
	}

	$user->remove_all_caps();

	$blogs = get_blogs_of_user($user_id);
	if ( count($blogs) == 0 ) {
		update_user_meta($user_id, 'primary_blog', '');
		update_user_meta($user_id, 'source_domain', '');
	}

	if ( $reassign != '' ) {
		$reassign = (int) $reassign;
		$post_ids = $wpdb->get_col( $wpdb->prepare( "SELECT ID FROM $wpdb->posts WHERE post_author = %d", $user_id ) );
		$link_ids = $wpdb->get_col( $wpdb->prepare( "SELECT link_id FROM $wpdb->links WHERE link_owner = %d", $user_id ) );

		if ( ! empty( $post_ids ) ) {
			$wpdb->query( $wpdb->prepare( "UPDATE $wpdb->posts SET post_author = %d WHERE post_author = %d", $reassign, $user_id ) );
			array_walk( $post_ids, 'clean_post_cache' );
		}

		if ( ! empty( $link_ids ) ) {
			$wpdb->query( $wpdb->prepare( "UPDATE $wpdb->links SET link_owner = %d WHERE link_owner = %d", $reassign, $user_id ) );
			array_walk( $link_ids, 'clean_bookmark_cache' );
		}
	}

	restore_current_blog();

	return true;
}