## 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

""" Tests designed for the many2many function field 'follower_ids'.
            We will test to perform writes using the many2many commands 0, 3, 4,
            5 and 6. """
        cr, uid, user_admin, partner_bert_id, group_pigs = self.cr, self.uid, self.user_admin, self.partner_bert_id, self.group_pigs
        
        group_dummy_id = self.mail_group.create(cr, uid,
            {'name': 'Dummy group'}, {'mail_create_nolog': True})
        self.mail_followers.create(cr, uid,
            {'res_model': 'mail.thread', 'res_id': self.group_pigs_id, 'partner_id': partner_bert_id})
        self.mail_followers.create(cr, uid,
            {'res_model': 'mail.group', 'res_id': group_dummy_id, 'partner_id': partner_bert_id})
        
        follower_ids = set([follower.id for follower in group_pigs.message_follower_ids])
        self.assertEqual(follower_ids, set([user_admin.partner_id.id]), 'Admin should be the only Pigs fan')
        
        group_pigs.write({'message_follower_ids': [(4, partner_bert_id)]})
        group_pigs.refresh()
        follower_ids = set([follower.id for follower in group_pigs.message_follower_ids])
        self.assertEqual(follower_ids, set([partner_bert_id, user_admin.partner_id.id]), 'Bert and Admin should be the only Pigs fans')
        
        group_pigs.write({'message_follower_ids': [(3, partner_bert_id)]})
        group_pigs.refresh()
        follower_ids = set([follower.id for follower in group_pigs.message_follower_ids])
        self.assertEqual(follower_ids, set([user_admin.partner_id.id]), 'Admin should be the only Pigs fan')
        
        group_pigs.write({'message_follower_ids': [(6, 0, [partner_bert_id])]})