## 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

signature = "--<br />%s" % user.name
            footer = tools.append_content_to_html(footer, signature, plaintext=False)
        
        if user.company_id.website:
            website_url = ('http://%s' % user.company_id.website) if not user.company_id.website.lower().startswith(('http:', 'https:')) \
                else user.company_id.website
            company = "<a style='color:inherit' href='%s'>%s</a>" % (website_url, user.company_id.name)
        else:
            company = user.company_id.name
        sent_by = _('Sent by %(company)s using %(odoo)s')
        signature_company = '<br /><small>%s</small>' % (sent_by % {
            'company': company,
            'odoo': "<a style='color:inherit' href='https://www.odoo.com/'>Odoo</a>"
        })
        footer = tools.append_content_to_html(footer, signature_company, plaintext=False, container_tag='div')
        return footer
    def update_message_notification(self, cr, uid, ids, message_id, partner_ids, context=None):
        existing_pids = set()
        new_pids = set()
        new_notif_ids = []
        for notification in self.browse(cr, uid, ids, context=context):
            existing_pids.add(notification.partner_id.id)
        
        self.write(cr, uid, ids, {'is_read': False}, context=context)
        
        new_pids = set(partner_ids) - existing_pids
        for new_pid in new_pids:
            new_notif_ids.append(self.create(cr, uid, {'message_id': message_id, 'partner_id': new_pid, 'is_read': False}, context=context))
        return new_notif_ids
    def _notify_email(self, cr, uid, ids, message_id, force_send=False, user_signature=True, context=None):