Hey,

try to keep a value of domain in a separate field. E.g.:

@api.multi
@api.depends("emeu_sector_id.emeu_education_ids")
def _get_education_domain(self):
        for object in self:
              education_list = []
              if object.emeu_sector_id.id:
                   education_ids = object.emeu_sector_id.emeu_education_ids
                   education_list = [x.id for x in education_ids]
              object.education_list =  [(6,0, education_list)]

education_list = fields.Many2many('emeu.education',store=True,compute=_get_education_domain)
emeu_education_id = fields.Many2one('emeu.education', string=_('Education'), ondelete='restrict'])

And on the xml form:

<field name="education_list" invisible="1"/> 
<field name="emeu_education_id" domain="[('id','in',education_list[0][2])]" />