An Etymological Dictionary of the German Language/Annotated/Scheune
Scheune, feminine (unknown to Upper German), ‘barn, shed,’ from the equivalent Middle High German schiune, feminine, which is derived by the loss of the g (equal to j?) from Old High German scugin, scugina, ‘barn.’ If the g is equal to j, Scheuer (Middle High German schiure) is closely allied. If this is not the case, No certain connecting link has been discovered.