## Impacted versions:
 8.0 / 9.0 / 10.0
## Steps to reproduce:
* see https://github.com/odoo/odoo/issues/11841
* in a shell
  1. create an in memory record `order = self.env['purcahse.order'].new({....})`
  2. create an in memory record with a reference to the first one `order_line = self.env['purchase.order.line'].new({'order_id': order, ....})`
  3. order_line.order_id is an in memory recordset
  4. create a record for a model that inherits from mail.thread `self.env['product.product'].create({....})`
  5. At this stage order_line.order_id is an empty recordset

## Current behavior:
 In memory records are dropped when a call is done to self.invalidate_cache
## Expected behavior:
In memory records are preserved when a call is done to self.invalidate_cache


There are lot of places where the method `invalidate_cache` is called and the silent removal of the in memory records from all environments has unpredictable effects on fields modified by a computed method or an onchange or even related fields .... Moreover since all caches are invalidated each time you create / write / unlink  (https://github.com/odoo/odoo/blob/10.0/addons/mail/models/mail_followers.py#L111) an instance of a model that inherits from 'mail.thread', the performances of the server are severely penalized.

OPW703903

body=_body2, type='email', subtype='mt_comment',
                        partner_ids=[p_d_id], parent_id=msg1_id, attachment_ids=[attach3_id],
                        context={'mail_post_autofollow': True})
        msg = self.mail_message.browse(cr, uid, msg2_id)
        msg_pids = [partner.id for partner in msg.notified_partner_ids]
        msg_aids = [attach.id for attach in msg.attachment_ids]
        sent_emails = self._build_email_kwargs_list
        # Test
        self.assertEqual(msg.subject, False, 'message_post: mail.message subject incorrect')
        self.assertEqual(msg.body, html_sanitize(_body2), 'message_post: mail.message body incorrect')
        self.assertEqual(msg.parent_id.id, msg1_id, 'message_post: mail.message parent_id incorrect')
        # Test
        test_pids = [self.partner_admin_id, p_d_id]
        self.assertEqual(set(test_pids), set(msg_pids), 'message_post: mail.message partners incorrect')
        # Test
        notif_ids = self.mail_notification.search(cr, uid, [('message_id', '=', msg2_id)])
        notif_pids = [notif.partner_id.id for notif in self.mail_notification.browse(cr, uid, notif_ids)]
        self.assertEqual(set(test_pids), set(notif_pids), 'message_post: mail.message notification partners incorrect')
        # Test
        self.assertFalse(self.mail_mail.search(cr, uid, [('mail_message_id', '=', msg2_id)]), 'mail.mail notifications should have been auto-deleted!')
        # Test
        test_emailto = [u'Administrator <a@a>', u'Bert Tartopoils <b@b>', u'Carine Poilvache <c@c>', u'D\xe9d\xe9 Grosbedon <d@d>']
        # test
        # self
        for sent_email in sent_emails:
            self.assertEqual(sent_email['email_from'], 'Raoul Grosbedon <r@r>',
                            'message_post: notification email wrong email_from: should use email of sender when no alias domain set')
            self.assertEqual(len(sent_email['email_to']), 1,
                            'message_post: notification email sent to more than one email address instead of a precise partner')
            self.assertIn(sent_email['email_to'][0], test_emailto,