[DonutOutputCache(
        Options = OutputCacheOptions.NoCacheLookupForPosts,
        Duration = 3600,
        Location = OutputCacheLocation.Server,
        VaryByParam = "calculationReference",
        VaryByCustom = "SurveySession(calculationReference)")]

    [AuthoriseIntermediaryInSameOrganisation("calculationReference")]
    [HttpGet]
    public ActionResult Details(string calculationReference)
    {
        .....

        return View(model);
    }

[HttpPost]
    public ActionResult CalculationNotes(CalculationNotesViewModel model)
    {
        if (!ModelState.IsValid)
        {
           ...
        }

       ...

        var cacheManager = new OutputCacheManager();
        cacheManager.RemoveItem("Calculation", "Details", new { calculationreference = model.CalculationId });

        return PartialView("_CalculationNotes", model);
    }