Deleted node-values shown as variable

I had add some nodes to Prometheus/grafana. After some days I deleted all dataset for only one node from prometheus (curl -X POST -g 'http://localhost:9090/api/v1/admin/tsdb/delete_series?match[]={node="..."}), but this node is still displayed in the node variable.
Does Grafana store the variable values anywhere? How can I delete this node-value completely?