How to remove all data from Sitecore Solr index ?

Challenge:

Few days back, was working on sitecore solr search related issue that 

From solr portal, was able to retrieve data from index even deleted items (solr index caching issue).

But in the code getting null value for item's properties.

Tried many alternatives to resolve issue (IISRESET, config review, code debug, index rebuild), but no luck.

Approach to fix above issue:

After removing all data from solr index, and then index rebuild issue was resolved.

Steps:

1. From browser open hosted solr portal

2. choose index

3. go to document tab

or copy below URL and hit

1. https://localhost:8987/solr/your_index_name/documents

after this

choose Document Type as Solr command (raw xml or JSON)

then paste query

<delete><query>*:*</query></delete>

and Submit document.