Add to array, redirect and display

If you need to pass some data over the redirect, you can do that by adding parameters to the redirect url with add_query_arg(). But other more elegant solutions might exist also.

Single parameter,

wp_redirect( add_query_arg( 'notice', 'success', get_site_url(null, '/redirect_to_two') ) );
exit;

or multiple parameters

wp_redirect( add_query_arg( array( 'notice' => 'success', 'foo' => 'bar' ), get_site_url(null, '/redirect_to_two') ) );
exit;

Then use $_GET to grab the parameter(s),

if ( ! empty( $_GET['notice'] ) && 'success' == $_GET['notice'] ) {
    // Do whatever.
}

If I’m not mistaken, I don’t think you need to worry about unsetting arrays as data doesn’t normally persist in WordPress. Once you do a redirect all the data in your $variables are gone.