bp_core_get_root_domain()

function bp_core_get_root_domain() {

	$domain = get_home_url( bp_get_root_blog_id() );

	/**
	 * Filters the domain for the root blog.
	 *
	 * @since BuddyPress 1.0.1
	 *
	 * @param string $domain The domain URL for the blog.
	 */
	return apply_filters( 'bp_core_get_root_domain', $domain );
}