## 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

_attachments_test = [('first.txt', 'My first attachment'), ('second.txt', 'My second attachment')]
        # 6 - Subscribe Bert to Pigs
        group_pigs.message_subscribe([p_b_id])
        
        # CASE1: wizard + partners + context keys
        
        # Do: Raoul wizard-composes on Pigs with auto-follow for partners, not for author
        compose_id = mail_compose.create(cr, user_raoul.id,
            {
                'subject': _subject,
                'body': _body,
                'partner_ids': [(4, p_c_id), (4, p_d_id)],
            }, context={
                'default_composition_mode': 'comment',
                'default_model': 'mail.group',
                'default_res_id': self.group_pigs_id,
            })
        compose = mail_compose.browse(cr, uid, compose_id)
        # Test: mail.compose.message: composition_mode, model, res_id
        self.assertEqual(compose.composition_mode,  'comment', 'compose wizard: mail.compose.message incorrect composition_mode')
        self.assertEqual(compose.model,  'mail.group', 'compose wizard: mail.compose.message incorrect model')
        self.assertEqual(compose.res_id, self.group_pigs_id, 'compose wizard: mail.compose.message incorrect res_id')
        # Do: Post the comment
        mail_compose.send_mail(cr, user_raoul.id, [compose_id], {'mail_post_autofollow': True, 'mail_create_nosubscribe': True})
        group_pigs.refresh()
        message = group_pigs.message_ids[0]
        # Test: mail.group: followers (c and d added by auto follow key; raoul not added by nosubscribe key)
        pigs_pids = [p.id for p in group_pigs.message_follower_ids]
        test_pids = [self.partner_admin_id, p_b_id, p_c_id, p_d_id]
        self.assertEqual(set(pigs_pids), set(test_pids),