Very simple question about cache

Hi,I set simply reverse proxy (backend is an Apache web server):
upstream backend { ip_hash; server 127.0.0.1:8080; }

server { listen x.y.w.z:80; # IP goes here. server_name
somedomain.com; expires off; location / {
proxy_pass http://backend; } real_ip_header
X-Forwarded-For;
# Set proxy headers for the passthrough proxy_set_header
Host $host; proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
access_log /var/log/nginx/domain.cache.log cache; access_log
/var/log/nginx/domain.access.log;}

While browsing website, I see lots on entry in
/var/log/nginx/domain.cache.log file (of course in
/var/log/nginx/domain.access.log too).My question is: with this
configuration, is there any caching active?

Example of cache log:
***05/Jul/2016:21:15:59 +0200 - Cache-Control: - Expires: -
some.domain.net “GET
/wp-admin/load-scripts.php?c=0&load%5B%5D=hoverIntent,common,admin-bar,wp-ajax-response,jquery-color,wp-lists,quicktags,jquery-query,admin-comments,jquery-ui-core,jquery-&load%5B%5D=ui-widget,jquery-ui-mouse,jquery-ui-sortable,postbox,dashboard,underscore,customize-base,customize-loader,thickbox,plugin-instal&load%5B%5D=l,shortcode,media-upload,svg-painter,heartbeat,wp-auth-check,wp-a11y,wplink,jquery-ui-position,jquery-ui-menu,jquery-ui-autocomp&load%5B%5D=lete&ver=4.5.3
HTTP/1.1” (304) “Mozilla/5.0 (Windows NT 10.0; WOW64; rv:47.0)
Gecko/20100101 Firefox/47.0” Args:
c=0&load%5B%5D=hoverIntent,common,admin-bar,wp-ajax-response,jquery-color,wp-lists,quicktags,jquery-query,admin-comments,jquery-ui-core,jquery-&load%5B%5D=ui-widget,jquery-ui-mouse,jquery-ui-sortable,postbox,dashboard,underscore,customize-base,customize-loader,thickbox,plugin-instal&load%5B%5D=l,shortcode,media-upload,svg-painter,heartbeat,wp-auth-check,wp-a11y,wplink,jquery-ui-position,jquery-ui-menu,jquery-ui-autocomp&load%5B%5D=lete&ver=4.5.3
Wordpress Auth Cookie: ***05/Jul/2016:21:16:59 +0200 - Cache-Control:
no-cache, must-revalidate, max-age=0 Expires: Wed, 11 Jan 1984 05:00:00
GMT some.domain.net “POST /wp-admin/admin-ajax.php HTTP/1.1” (200)
“Mozilla/5.0 (Windows NT 10.0; WOW64; rv:47.0) Gecko/20100101
Firefox/47.0” Args: - Wordpress Auth Cookie: ***05/Jul/2016:21:18:59
+0200 - Cache-Control: no-cache, must-revalidate, max-age=0 Expires:
Wed, 11 Jan 1984 05:00:00 GMT some.domain.net “POST
/wp-admin/admin-ajax.php HTTP/1.1” (200) “Mozilla/5.0 (Windows NT 10.0;
WOW64; rv:47.0) Gecko/20100101 Firefox/47.0” Args: - Wordpress Auth
Cookie: