There are two ways you can get the cache cleared for the assets with AEM DM Hybrid setup:
1. In AEM you can change the Default Manifest setting for the image server. You can fine-tune quality (JPEG quality, resolution, resampling mode), caching (expiration), and prevent the rendering of images that are too large (defaultpix, defaultthumbpix, maxpix). More detailed information can be found here[0]
2. Open a support ticket along with the list of asset URLs and will get that processed from the backend.
[0] https://docs.adobe.com/content/help/en/experience-manager-64/assets/dynamic/config-dynamic.html#defa...
I hope this helps