Do not include custom markdown pages as top-level pages when including them as subpage?

Question

I include markdown files in my groups in doxygen like so:

/**
 * @addtogroup foobar "Foo Bar"
 * @{
 * @subpage doc_foo_bar
 */

And they show up in the module documentation as requested. But anyways, they show up as normal top-level-pages, like so:

project
 - foo_bar   <-- The "doc_foo_bar" custom markdown page
 - modules
 - - foobar  <-- The module "foobar", which includes a "detailed documentation", which links to the markdown page

How to remove the top-level markdown page if it is already included in the module documentation group?

I hope my explanation is plain.