gistfile1.el

(defadvice delete-file (before purge-from-projectile-cache (filename &optional trash))
  (if (and (projectile-project-p) projectile-enable-caching)
      (let* ((project-root (projectile-project-root))
             (true-filename (file-truename filename))
             (relative-filename (file-relative-name true-filename project-root)))
        (if (projectile-file-cached-p relative-filename project-root)
            (projectile-purge-file-from-cache relative-filename)))))