How do I remove a pet stain from a sisal rug?

I returned from a trip to find the dog had vomited on my sisal rug. The pet sitter put paper towels to soak it up so the stain had plenty of time to set. I've tried blotting it with a water-soaked towel and that seemed to help, but there still is a large, dark stain.

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Sisal Rugs|Rugs